Practically, smart cards are divided into two categories.
Smart cards of a first category use contact pads to connect electrically the microcontroller to the outside world.
Smart cards of a second category use radio frequency waves to communicate. They comprise a radio frequency microcontroller electrically connected to an antenna.
In FIG. 1, a schematic conventional contactless smart card 10 is illustrated. The manufacture of contactless smart cards is usually based on a semi-finished product often called “pre-laminated inlet” 11. The inlet is usually made of at least four layers that are laminated. These layers comprise two layers 1 and 2 of plastic sheet, made of poly-vinyl-chloride (PVC) for example, and two overlays layers 3 and 4. The inlet 11 hosts a copper wired antenna 5 connected to the contact pads of an electronic module 6, by thermo-compression welding, or other mean such as a conductive glue. Then, at least one pre-printed layer 8, 9, made of PVC for example, and at least one overlay layer 12, 13 are laminated with the inlet 11. The pre-printed design is generally made by offset printing process, for decorative or advertising purposes. The thickness of the pre-printed layers 8, 9 is generally 150 μm and the thickness of the overlays 12, 13 is generally 50 μm.
FIG. 2 is a schematic conventional smart card 20 with contact pads 21 which are substantially flush with one of the main surfaces 22 of the smart card. The manufacture of such smart cards is usually based on a plastic sheet 11, made of poly-vinyl-chloride (PVC), or acrylonitrile-butadiene-styrene (ABS) for example. The plastic sheet 11 is laminated between at least one pre-printed plastic sheet 8, 9 and two or more overlay layers 12, 13 that are generally 50 μm thick. Then, a cavity 24 is provided in the thus obtained plastic card body in order to affix an electronic module 25 in such a manner that contact pads 21 are flush with one main surface 22.
Other conventional processes may also be used to manufacture a smart card. For example, the card may be manufactured by injection, in a mold, of a molten plastic material and then, solidification and unmolding of the thus obtained card body. The printing process of the card body is then performed before the lamination process of the overlays.
In all conventional processes for producing smart cards, at least one pre-printed layer is laminated between an overlay layer and the plastic sheet constituting the card body.
Nowadays, there is a strong request for making smart cards which have an improved appearance, and particularly smart cards having a printed surface with optical effects. Namely, such optical effects are particularly requested because they give the card a very distinguishable aspect and a high promotion value that reflects a prestigious image.
In this context, it has been tried to make smart cards having a surface with a pearlescent effect. For that, pearlescent transparent varnishes that are currently commercialized have been applied on the main surface of at least one pre-printed layer constituting smart card.
However, it appears that existing pearlescent varnishes are not suitable for printing smart cards. Namely, they do not provide the requisite pearlescent effect. In fact, there is no variation of the coloration of the pigment used in the varnishes with the tilt angle of the card, so that there is no variation of the light refraction with the tilt of the card.
Moreover, the adherence of the laminated overlays on the surface of the card is bad and overlays are therefore easily delaminated or torn off.
Due to these drawbacks, the manufacture of smart cards having such printed surfaces does not satisfy customers and leads to financial losses, because of great number of wasted card, and complaint from unhappy customers.